1. Field of the Invention
The present invention relates to a storage device which positions a head at a target location on a storage medium, and a method of controlling a spindle motor of the storage device.
2. Description of the Related Art
A computer device has incorporated therein or connected thereto a storage device, such as a magnetic disk device, that has incorporated therein a disk-like storage medium and reads and writes information therefrom and thereto. In such a storage device, with the rotation of the storage medium by a spindle motor (SPM) and sliding of an actuator having a head mounted thereon by a voice coil motor (VCM) for reading and writing information from and to the storage medium, the head is positioned at a target location on the storage medium.
Here, to position the head at the target location to read and write information from and to the storage medium, the number of rotations of the storage medium has to reach a steady state. However, in relation to the moment of inertia of the storage medium and the driving force of the SPM according to the current amount to be applied to the SPM, it may take some time for the number of rotations of the storage medium to reach the steady state after the storage device is powered up, making it impossible to quickly activate the storage device and also impossible to quickly position the head at the target location on the storage medium.
To get around this problem, in an SPM control method as disclosed in Japanese Patent Application Laid-open Publication No. 2005-237195, the power supply voltage value supplied to the SPM is measured and, according to the measured power supply voltage, a maximum current value that can be supplied to the SPM within maximum allowable power of the storage device. With an SPM activating current corresponding to this calculated maximum current value being applied to the SPM, the SPM can be activated more quickly.
However, the conventional technologies typified by the one disclosed in Japanese Patent Application Laid-open Publication No. 2005-237195 have the following problems. That is, since power is represented by the product of a resistance value and a current amount, if the resistance value is constant, the maximum allowable power of the storage device is directly proportional to the square of the current amount that can be allowed to be applied to the storage device. Conversely, if the maximum allowable power is set as being constant, the current that can be allowed to be applied to the storage device is determined accordingly.
Here, the maximum allowable power of the storage device is required to be set most conservatively so as to prevent a failure of the storage device. Therefore, to minimize the maximum allowable power of the storage device within the range of an assumed environment where the storage device is used, the current amount that can be allowed to be applied to the storage device is required to be minimized.
If the power supply voltage supplied to the storage device is constant, with small maximum allowable power, the current amount that can be applied to the storage device, particularly the SPM, has to be decreased. If the current amount that can be applied to the SPM is small, the time from the start of the rotation of the SPM until the rotation reaches the steady state is increased, also making it impossible to quickly activate the storage device and also impossible to quickly position the head at the target location on the storage medium.